Liquid manure spreading machines have been developed to spread animal manures on the soil. These machines have a tank mounted on a trailer towed by a vehicle, as a tractor. A pump operated by the tractor functions to selectively apply air pressure or withdraw air from the tank. The tank is filled by suction forces applied to a fill hose connected to the tank. The material is spread by applying air under pressure to the tank. An example of this type of machine is shown in U.S. Pat. No. 3,523,612. The pump in some air pressure tank spreaders is connected to the tank with an air pressure line and a separate vacuum line. The pump is an air pump which will become inoperable, damaged and in most cases destroyed when liquid foam, or manures enter the pump. Safety shut off valves are used to protect against liquids, manures and foam from entering the pump. These valves have been ineffective in eliminating the entry of these materials into the pumps. The result is that the pumps become inoperative and must be repaired or replaced.